Depolarizing homogenizer

ABSTRACT

A depolarizing homogenizer including one or more lenslet arrays, for providing a plurality of beamlets associated with different respective parts of a received beam. The depolarizing homogenizer includes a depolarizer comprising different areas which affect polarization differently, the depolarizer being positioned to cause alteration of the polarization characteristics of at least some of the plurality of beamlets. A lens is arranged to at least partially overlap the beamlets having the altered polarization characteristics.

FIELD

This specification relates to a depolarizing homogenizer, and to a lightsource comprising a depolarizing homogenizer. In some examples the lightsource includes a supercontinuum source.

BACKGROUND

Depolarizers in the form of patterned retarders or quartz-wedgedepolarizers alter the polarization characteristics of a received beamof light to provide a depolarized output beam. Such depolarizers convertthe received beam into a pseudo-random polarized beam, i.e. thepolarization varies spatially in a cross section of the beamperpendicular to the beam path.

This variation of the polarization characteristics across the beamprofile may not be desired in some applications which employ depolarizedbeams.

SUMMARY

This specification provides a depolarizing homogenizer. The depolarizinghomogenizer includes one or more lenslet arrays, adapted for providing aplurality of beamlets associated with different respective parts of areceived beam. The depolarizing homogenizer also includes a depolarizercomprising different areas which affect polarization differently. Thedepolarizer is positioned to cause alteration of the polarizationcharacteristics of at least some of said plurality of beamlets. Thedepolarizing homogenizer also includes a lens arranged to at leastpartially overlap the said beamlets having said altered polarizationcharacteristics.

By at least partially overlapping beamlets having altered polarizationcharacteristics, an output beam is produced having a high degree ofdepolarization. In particular, the degree of depolarization may besubstantially uniform over a cross section of the beam perpendicular tothe beam path (or a substantial region thereof). In other words, thedegree of depolarization may be substantially uniform over a substantialregion of the beam profile.

The received beam may be coherent, incoherent or partly coherent(temporally and/or spatially). In the case of a coherent beam, thedepolarizer may additionally help reduce interference fringes (speckleeffect), because beams from individual lenslets having differentpolarizations may not interfere in the image plane of the lens.

The depolarizer may comprise a liquid crystal polymer or a quartzcrystal wedge depolarizer. In some embodiments the depolarizer maycomprise an electronically controlled liquid crystal depolarizer, whichmay be configured to change polarization characteristics of differentparts of the depolarizer in time.

The depolarizer may comprise a first depolarizing element having a firstoptic axis and a second depolarizing element have a second optic axis,wherein the first and second depolarizing elements are oriented suchthat the first and second optic axes are perpendicular to one another.In the case of a quartz crystal wedge depolarizer comprising two quartzcrystal wedges, one thicker than the other, the optic axis may bedefined by the optic axis of the thicker wedge. In the case of a liquidcrystal polymer depolarizer comprising retardation lines, the optic axismay be defined by the retardation lines. Thus, two liquid crystalpolymer depolarizers may be oriented such that their respective firstand second optic axes are perpendicular by orienting the twodepolarizers so that equal retardation lines of respective depolarizersare perpendicular to one another.

The depolarizer may be positioned to receive said plurality of beamlets,wherein at least some of said beamlets pass through respective differentareas of the depolarizer, thereby to alter the polarizationcharacteristics of said at least some beamlets. The depolarizer may belocated between the one or more lenslet arrays and the lens.Alternatively, the lens may be located between the one or more lensletarrays and the depolarizer.

Further alternatively, the depolarizer may be configured to depolariselight before the light passes through the one or more lenslet arrays toform said plurality of beamlets, thereby to cause alteration of thepolarization characteristics of at least some of said plurality ofbeamlets. In some example configurations the one or more lenslet arraysmay be located between the depolarizer and the lens.

The depolarizing homogenizer may further comprise a fibre bundle,wherein the fibre bundle includes a plurality of optical fibres forguiding light. The depolarizer may be located between an output of thefibre bundle and the image plane of the lens. The depolarizinghomogenizer may include a collimating lens to receive light from thefibre bundle and to collimate the received light. The one or morelenslet arrays may be arranged to receive light which has beencollimated by the collimating lens.

A lenslet array may comprise a plurality of lenslets arranged in a planewhich is perpendicular to the direction of the received beam.

The lenslets may comprise microlenses, e.g. cylindrical microlenses.

The focal lengths of the lenslets in a lenslet array may be the sameand/or one or more lenslets of one lenslet array may have the same focallength as one or more lenslets of a second lenslet array.

The one or more lenslet arrays may comprise a plurality of lensletsshaped to cause the output beam to have a flat top beam profile.

The one or more lenslet arrays may comprise a plurality of lensletsshaped to cause the output beam to have a square or rectangular beamprofile.

The one or more lenslet arrays may comprise a first lenslet array and asecond lenslet array. The first and second lenslet arrays may be spacedapart. The spacing may be less than the focal length of one of morelenslets in the first and/or the second array.

The first and second lenslet arrays may be oriented at an angle (e.g.perpendicular) to one other. In the case of first and second lensletsarrays having respective non-symmetric lenslets (e.g. cylindricalmicrolenses), the first and second lenslet arrays may be oriented withrespect to one another so that the lenslets of the respective arrays areoriented at an angle (e.g. perpendicular) to one another.

The beamlets may be collimated.

The lens may be configured to form overlapping images of the lensletarray cells in an image plane. The image plane may comprise a worksurface.

This specification also provides a light source comprising thedepolarizing homogenizer. The light source may include a linearlypolarized or partially linearly polarized source. The beam received bythe one or more lenslet arrays of the depolarizing homogenizer may bederived from said linearly polarized or partially linearly polarizedsource.

In some embodiments the light source includes a supercontinuum sourceconfigured to generate a supercontinuum, wherein the beam received bythe one or more lenslet arrays of the depolarizing homogenizer isderived from said supercontinuum source. In various embodiments thesupercontinuum spectrum that is generated includes the wavelength range375 nm to 1200 nm. In some embodiments the supercontinuum io spectrumthat is generated includes the wavelength range 375 nm to 2400 nm. Insome embodiments the supercontinuum that is generated may comprise amid-infrared supercontinuum which may include the wavelength range 1100nm to 4200 nm. The light source may further comprise a wavelengthselector to select one or more wavelengths from the supercontinuum.

In various embodiments the output beam may have a polarizationextinction ratio of 1 dB or less, 0.5 dB or less, 0.1 dB or less, or0.05 dB or less.

This specification also provides a depolarization method, comprisingdividing received light into a plurality of beamlets, causing alterationof the polarization characteristics of at least some of said pluralityof beamlets, and providing a depolarized output beam by at leastpartially overlapping the beamlets having said altered polarizationcharacteristics.

The method may comprise altering the polarization characteristics of atleast some of said plurality of beamlets after said plurality ofbeamlets have been divided from said received light. Alternatively, themethod may comprise depolarizing the received light before it isdivided, thereby altering the polarization characteristics of at leastsome of said plurality of beamlets.

The specification also provides an optical arrangement configured tocarry out the method.

This specification also provides a light source. The light source cancomprise a supercontinuum source for generating a supercontinuum, awavelength selector for selecting light at one or more wavelengths fromthe supercontinuum, and a fibre bundle comprising a plurality of opticalfibres arranged to guide light selected by the wavelength selector, andto output light at the one or more selected wavelengths, and adepolarizing homogenizer configured to receive light which has beenoutput by the fibre bundle.

As will be understood by those skilled in the art, the term “light” asused herein is not limited to visible light and instead includes anysuitable electromagnetic radiation such as infrared light (includingnear and far infrared light), visible light and ultraviolet light.

BRIEF DESCRIPTION OF THE FIGURES

Example embodiments will now be described with reference to theaccompanying figures, in which:

FIG. 1 is a schematic illustration of a light source according to oneexample embodiment;

FIG. 2(a) is a schematic illustration showing components of adepolarizing homogenizer in accordance with one example embodiment;

FIG. 2(b) is a schematic illustration showing components of adepolarizing homogenizer in accordance with an example embodiment;

FIG. 2(c) is a schematic illustration showing components of adepolarizing homogenizer in accordance with an example embodiment;

FIG. 3 shows the polarization distribution of a linearly polarizedmonochromatic beam after it has been passed through a quartz crystaldepolarizer;

FIG. 4 shows the result of a beam profile measurement of the output beamof the system of FIG. 2(a) after has been passed through a polarizer;and

FIG. 5a shows the results of polarization extinction ratio measurements.

FIG. 5b is a close-up of a region of the graph of FIG. 5 a.

DETAILED DESCRIPTION

FIG. 1 shows a light source 1 according to one example. As shown, thelight source includes a supercontinuum source 10, a wavelength selectionmodule 20, a coupling module 25, a fibre bundle 30 and an optical head40.

The supercontinuum source 10 comprises a source which generates abroadband spectral output in the form of a supercontinuum.Supercontinuum generation is known per se and will not be described indetail here. Reference is directed to “Visible continuum generation inair silica microstructure optical fibres with anomalous dispersion at800 nm”, J. K. Ranka, R. S. Windeler, and A. J. Stentz, Optics Letters,2000. Vol. 25: p. 25-27. An exemplary commercially-availablesupercontinuum source is the SuperK Extreme EXU-6 source from NKTPhotonics A/S. In a supercontinuum source, the temporal coherence may below and the spatial coherence may be high. That is, the supercontinuumlight may be spatially coherent and temporally incoherent.

The wavelength selection module 20 is configured to select one or morewavelengths w from the broadband output produced by the supercontinuumsource 10. In the example of FIG. 1, the wavelength selection module isa tunable multi-wavelength filter based on an acousto-optic filter. Anexemplary commercially available tunable multi-wavelength filter basedon acousto-optic tunable filter technology is the SuperK SELECT productfrom NKT Photonics A/S. The output of the wavelength selection modulemay be linearly polarized. The temporal coherence of the output may below, e.g. the output may be temporally incoherent. The supercontinuumspectrum that is generated may include the range 375 nm to 1200 nm. Insome example implementations the bandwidth of the supercontinuum mayextend from 375 nm to 2400 nm. In some example implementations thesupercontinuum that is generated may comprise a mid-infraredsupercontinuum which may extend from 1100 nm to 4200 nm.

The light source 1 further comprises a coupling module 25 arranged tocouple the one or more wavelengths selected by the wavelength selectionmodule 20 into a fibre bundle 30. The coupling module 25 may include ahomogenizing light pipe (HLP) in the form of an elongated rod or tubecapable of propagating light and of homogenizing the intensitydistribution of the propagated light. The HLP may comprise alight-guiding region comprising a transparent medium withcross-sectional dimensions greater than the wavelength(s) of the guidedlight. The HLP may be formed by appropriately shaping a dielectricmedium (e.g. forming a polygonal glass rod), or by providing a tubularwall with a reflective inner surface, which defines the light-guidingregion and which typically has an appropriate rotationally asymmetric(i.e. non-circular) cross-section that homogenizes the light irradianceby multiple reflections off the boundary or boundaries of the HLP.

Light from the wavelength selection module 20 may be coupled into aninput end of the HLP of the coupling module, e.g. via free space opticsand/or via an optical fibre. The exit end of the HLP may be butt coupledto the common packed input end of the fibre bundle 30. The fibre bundle30 comprises a plurality of optical fibres (e.g. a plurality ofmultimode fibres) which guide light at the wavelengths selected by thewavelength selector.

The fibre bundle 30 is terminated with the optical head 40. Componentsof the optical head are shown in FIG. 2(a). As show, a fiber bundleferule 41 is located at the input of the optical head. The fiber bundleferule emits a divergent beam, which is received at a collimating lens42 which collimates the beam. The collimated beam then passes throughtwo lenslet arrays in the form of cylindrical microlens arrays 43 a , 43b . An imaging lens 44 (which may also be referred to herein as a“Fourier lens” or a “focusing lens”), is arranged to form an image inimage plane 46. A depolarizer 47 is located between the lenslet arraysand the imaging lens 44.

The depolarizer 47 may comprise a patterned retarder in the form of anachromatic liquid crystal polymer depolarizer. Alternatively, or inaddition, the depolarizer may comprise a quartz crystal wedgedepolarizer. Achromatic liquid crystal polymer depolarizers and quartzcrystal wedge depolarizers are known per se and will not be described indetail here: suitable depolarizers are commercially available fromThorlabs under product numbers DPP25-A and DPU25-A. In general, suchdepolarizers comprise different areas which affect polarizationdifferently. Hence, if a linearly polarized monochromatic beam having abeamwidth which spans multiple of these areas is passed through such adepolarizer, the polarization of different regions of the beam profilewill be altered in different ways, resulting in variation of thepolarization in a cross section perpendicular to the beam direction;this is illustrated schematically in FIG. 3.

In contrast, in the arrangement of FIG. 2(a), the microlenses of thecylindrical microlens arrays 43 a , 43 b are configured to form aplurality of beamlets associated with different respective parts of thereceived beam. In FIG. 2(a), the depolarizer is positioned after themicrolens arrays 43 a , 43 b so that beamlets pass through respectivedifferent areas of the depolarizer and are therefore subject todifferent polarization retardation. The imaging lens 44 is configured toform overlapping images of the microlens array cells in the same regionof the image plane. Thus, the beamlets, which have been subjected todifferent polarization retardation, are scrambled in the image plane,resulting in an output beam having a high degree of depolarizationuniformly distributed across the beam. In one embodiment, contributionsto depolarization are also provided by changes in polarizationcharacteristics resulting from propagation through the fiber bundle, andother optical components of the light source 1.

In addition, the arrangement of the cylindrical microlens arrays 43 a ,43 b and imaging lens 44 acts as an intensity homogenizer, i.e. ithomogenizes the intensity across the beam profile. This is because theimaging lens 44 is configured to form overlapping images of thebeamlets, and therefore the intensity profiles of individual beamletsassociated with different parts of the received beam are “averaged out”in the image plane, resulting in an output beam with a homogenizedintensity profile.

The beam profile of the output beam is determined by the shape of thelenslets. For example, the lenslets in the lenslet arrays may be shapedso that the image which is formed in the image plane is of a flat top(e.g. square) homogenized beam. The homogenizing light pipe discussedabove also contributes to the degree of homogenization of the outputbeam.

FIG. 4 shows the result of a beam profile measurement of the output beamof the system of FIG. 2(a) after has been passed through a polarizer. Asshown a homogenized intensity distribution is obtained. In contrast,significant intensity variations would be expected if there weresignificant polarization change across the beam.

In order to measure the polarization extinction ratio (PER) of thesystem of FIG. 2(a), the output of the optical head 40 was directedthrough a polarizer into a power meter. By rotating the polarizer themaximum and minimum powers (Pmax and Pmin) were measured, and thepolarization extinction ratio, given by 10Log₁₀(Pmax/Pmin) wascalculated. The procedure was repeated at different wavelengths byselecting different wavelengths using the wavelength selection module20. The results are shown in FIGS. 5a and 5 b, which show measurementresults for 3 cases: no depolarizer, liquid crystal polymer depolarizer(DPP25-A) and quartz crystal wedge depolarizer (DPU25-A). As shown,using a quartz crystal wedge depolarizer, a polarization extinctionratio of less than 0.04 dB was achieved in the range 400 nm to 700 nm

Although FIG. 2(a) shows the depolarizer located between the microlensarrays and the imaging lens, alternatively the imaging lens may belocated between the microlens arrays and the depolarizer. Thisalternative configured is illustrated in FIG. 2(c). Positioning thedepolarizer immediately after the imaging lens (rather than before theimaging lens) did not affect the measurement results shown in FIGS. 5aand 5 b.

In a further alternative embodiment, the depolarizer may be locatedupstream of the microlens arrays, between the collimating lens and themicrolens arrays. In this case light passes through the depolarizerbefore it passes through the one or more microlens arrays to form saidplurality of beamlets. In this configuration the depolarizer providesthe beam with a polarization which is different in different regions ofthe beam profile, before the beam is divided into beamlets by themicrolens arrays. In this way, the presence of the depolarizer causesalteration of the polarization characteristics of the beamlets, suchthat different beamlets have different polarization characteristics. Thebeamlets are then brought into overlap and in the image plane by theimaging lens 44 so as to obtain a high degree of depolarizationuniformly distributed across the beam profile.

As will be understood from the foregoing, in various embodiments adepolarizing homogenizer is provided comprising one or more lensletarrays (e.g. one or more microlens arrays), a depolarizer, and a lens.The lenslet array(s) are adapted for providing a plurality of beamletsassociated with different respective parts of a received beam. Thedepolarizer is positioned, either upstream or downstream of the lensletarray(s), to cause alteration of the polarization characteristics of atleast some of the plurality of beamlets. The lens is arranged to atleast partially overlap the beamlets having said altered polarizationcharacteristics, to provide an output beam. In various embodiments theoutput beam has a high degree of depolarization uniformly distributedacross the profile of the beam

Although two successive lenslet arrays may be employed in someembodiments (e.g. as shown in FIG. 2(a)), in other embodiments a singlelenslet array may be employed (e.g. as shown in FIG. 2(b). Moreoveralthough a single depolarizing element may be employed in someembodiments, in some embodiments an even higher degree of depolarizationmay be achieved by placing two depolarizing elements with optical axisperpendicular to each other. The depolarizer may thus comprise one ormore liquid crystal polymers, one or more quartz crystal wedgedepolarizers, or a combination of one or more liquid crystal polymersand one or more quartz crystal wedge depolarizers.

Although FIG. 2(a) shows a depolarizing homogenizer used in conjunctionwith a supercontinuum source having a wavelength selection module, acoupling module and a fiber bundle, the depolarizing homogenizer may beemployed in conjunction with any suitable supercontinuum source. Forexample in some embodiments one or more, including all, of thewavelength selection module, coupling module and fiber bundle may beomitted. For example, in some embodiments the depolarizing homogenizerio may be used in conjunction with a supercontinuum source which doesnot employ a wavelength selector, but employs a coupling module and/orfiber bundle.

Moreover depolarizing homogenizers according to various embodiments mayalternatively be used in conjunction with other linearly or partlylinearly polarized sources such as a narrowband single wavelength,tunable or other broadband light sources. For example, in variousembodiments the depolarizing homogenizer may be used in conjunction witha single wavelength laser, tunable laser, LED, or other suitable source.

Many further modifications and variations will be evident to thoseskilled in the art, that fall within the scope of the following claims:

1. A depolarizing homogenizer, comprising: one or more lenslet arrays,adapted for providing a plurality of beamlets associated with differentrespective parts of a received beam; a depolarizer comprising differentareas which affect polarization differently, wherein the depolarizer ispositioned to cause alteration of the polarization characteristics of atleast some of said plurality of beamlets; and a lens arranged to atleast partially overlap the said beamlets having said alteredpolarization characteristics, to provide an output beam.
 2. Adepolarizing homogenizer according to claim 1, wherein the depolarizeris positioned to receive said plurality of beamlets, wherein at leastsome of said beamlets pass through respective different areas of thedepolarizer, thereby to alter the polarization characteristics of saidat least some beamlets.
 3. A depolarizing homogenizer according to claim1 or claim 2, wherein the depolarizer is located between at least one ofthe one or more lenslet arrays and the lens.
 4. A depolarizinghomogenizer according to claim 1 or claim 2, wherein the lens is locatedbetween at least one of the one or more lenslet arrays and thedepolarizer.
 5. A depolarizing homogenizer according to claim 1, whereinthe depolarizer is configured to depolarise light before the lightpasses through the one or more lenslet arrays to form said plurality ofbeamlets, thereby to cause alteration of the polarizationcharacteristics of at least some of said plurality of beamlets.
 6. Adepolarizing homogenizer according to claim 1 or claim 5, wherein saidone or more lenslet arrays is located between the depolarizer and thelens.
 7. A depolarizing homogenizer according to any one of thepreceding claims, wherein the depolarizer comprises a liquid crystalpolymer or a quartz crystal wedge depolarizer.
 8. A depolarizinghomogenizer according to any one of the preceding claims, wherein thedepolarizer comprises a first depolarizing element having a first opticaxis and a second depolarizing element have a second optic axis, whereinthe first and second depolarizing elements are oriented such that thefirst and second optic axes are at an angle to one another, whereinoptionally the first and second depolarizing elements are oriented suchthat the first and second optic axes are perpendicular to one another.9. A depolarizing homogenizer according to any one of the precedingclaims, further comprising a fibre bundle, wherein the fibre bundleincludes a plurality of optical fibres for guiding light, wherein thedepolarizer is located between an output of the fibre bundle and animage plane of the lens.
 10. A depolarizing homogenizer as claimed inclaim 9, further comprising a collimating lens to receive light from thefibre bundle and to collimate the received light, wherein the one ormore lenslet arrays are arranged to receive light which has beencollimated by the collimating lens.
 11. A depolarizing homogenizer asclaimed in any one of the preceding claims, wherein the one or morelenslet arrays comprise a plurality of lenslets shaped to cause theoutput beam to have a flat intensity beam profile in an image plane ofthe lens.
 12. A depolarizing homogenizer as claimed in any one of thepreceding claims, wherein the one or more lenslet arrays comprise aplurality of lenslets shaped to cause the output beam to have a squareor rectangular beam profile.
 13. A depolarizing homogenizer as claimedin any one of the preceding claims, wherein the one or more lensletarrays comprise a first lenslet array and a second lenslet array,wherein the first and second lenslet arrays are oriented perpendicularlywith respect to one another.
 14. A depolarizing homogenizer as claimedin any preceding claim, wherein the depolarizer comprises anelectronically controlled liquid crystal depolarizer.
 15. A light sourcecomprising a depolarizing homogenizer according to any one of thepreceding claims.
 16. A light source as claimed in claim 15, wherein thelight source includes a linearly polarized or partially linearlypolarized source, wherein the beam received by the one or more lensletarrays of the depolarizing homogenizer is derived from said linearlypolarized or partially linearly polarized source.
 17. A light source asclaimed in claim 15 or claim 16, wherein the light source includes asupercontinuum source configured to generate a supercontinuum, whereinthe beam received by the one or more lenslet arrays of the depolarizinghomogenizer is derived from said supercontinuum source.
 18. A lightsource as claimed in claim 17, wherein the supercontinuum includes thewavelength range 375 nm to 1200 nm.
 19. A light source as claimed inclaim 17 or claim 18, wherein the supercontinuum includes the wavelengthrange 375 nm to 2400 nm.
 20. A light source as claimed in any one ofclaims 17 to 19, wherein the supercontinuum includes the wavelengthrange 1100 nm to 4200 nm.
 21. A light source according to any one ofclaims 17 to 20, wherein the light source further comprises a wavelengthselector to select one or more wavelengths from the supercontinuum. 22.A light source according to any one of claims 15 to 21, wherein theoutput beam has a polarization extinction ratio of 1 dB or less, 0.5 dBor less, 0.1 dB or less, or 0.05 dB or less.
 23. A depolarizationmethod, comprising: dividing received light into a plurality ofbeamlets; causing alteration of the polarization characteristics of atleast some of said plurality of beamlets; providing a depolarized outputbeam by at least partially overlapping the beamlets having said alteredpolarization characteristics.
 24. The depolarization method as claimedin claim 23, comprising altering the polarization characteristics of atleast some of said plurality of beamlets after said plurality ofbeamlets have been divided from said received light.
 25. Adepolarization method as claimed in claim 23, comprising depolarizingthe received light before it is divided, thereby altering thepolarization characteristics of at least some of said plurality ofbeamlets.
 26. A depolarization method as claimed in any one of claims 23to 25, wherein the depolarized output beam has a flat top beam profile.27. A depolarization method as claimed in any one of claims 23 to 26,wherein the depolarized output beam has a square beam profile.
 28. Adepolarization method as claimed in any one of claims 23 to 27, whereinthe depolarized output beam has a polarization extinction ratio of idBor less, 0.5 dB or less, 0.1 dB or less, or 0.05 dB or less.
 29. A lightsource, comprising: a supercontinuum source for generating asupercontinuum; a wavelength selector for selecting light at one or morewavelengths from the supercontinuum; a fibre bundle comprising aplurality of optical fibres arranged to guide light selected by thewavelength selector, and to output light at the one or more selectedwavelengths; a depolarizing homogenizer configured to receive lightwhich has been output by the fibre bundle, wherein the depolarizinghomogenizer comprises: one or more lenslet arrays, for providing aplurality of beamlets associated with different respective parts of abeam received at the one or more lenslet arrays; a depolarizercomprising different areas which affect polarization differently,wherein the depolarizer is positioned to cause alteration of thepolarization characteristics of at least some of said plurality ofbeamlets; and a lens arranged to at least partially overlap the saidbeamlets having said altered polarization characteristics, to provide anoutput beam.
 30. A light source as claimed in claim 29, wherein thesupercontinuum includes the wavelength range 375 nm to 1200 nm.
 31. Alight source as claimed in claim 29 or claim 30, wherein thesupercontinuum includes the wavelength range 375 nm to 2400 nm.
 32. Alight source as claimed in any one of claims 29 to 31, wherein thesupercontinuum includes the wavelength range 1100 nm to 4200 nm.